The present invention relates to an add-drop multiplexer having a plurality of interface circuits for high and low speed side transmission lines for dropping a multiplexing signal from a high speed side signal and inserting a multiplexing signal into a high speed side signal, and more particularly to an add-drop multiplexer capable of linking a multiplexing signal between low speed side transmission circuits.
A conventional add-drop multiplexer capable of linking a multiplexing signal between low speed side transmission circuits may include a cross connect device having interface circuits for two high speed transmission lines and for a plurality of low speed transmission circuits. The cross connect device can link a multiplexing signal between arbitrary transmission lines so that a multiplexing signal can be linked between low speed side transmission lines.